⇒ Concubine has been sometimes, but rarely, used of a male paramour as well as of a female.

Trench.

2.

A wife of inferior condition; a lawful wife, but not united to the man by the usual ceremonies, and of inferior condition. Such were Hagar and Keturah, the concubines of Abraham; and such concubines were allowed by the Roman laws. Their children were not heirs of their father.